1. Field of the Invention
The present invention relates to a control apparatus for an electric rotating machine which is mounted as a main engine on a vehicle together with a power conversion circuit to be connected to the electric rotating machine, and a cooling apparatus for circulating coolant to the electric rotating machine and the power conversion circuit through a circulation channel.
2. Description of Related Art
As described, for example, in Japanese Patent Application Laid-open No. 2006-211886, there is known a torque-limiting device for limiting the torque of a motor when the temperature of an inverter connected as a power conversion circuit to the motor is high. The torque-limiting device enables to reduce an amount of heat generation of switching elements included in the inverter to prevent the temperature of the inverter from further increasing.
However, for the torque-limiting device to operate, it is necessary to provide a data transmitting means for transmitting data indicative of the temperature of the inverter to a control apparatus. When the inverter is mounted on a vehicle, the data transmitting means has to include an insulating means such as photocouplers and a signal processing means for modulating the data to signals appropriate to be transmitted through the insulating means, because the reference potential of the vehicle-mounted inverter is different from that of the control apparatus which manipulates the vehicle-mounted inverter.
Meanwhile, if a cooling apparatus for the inverter has a large enough capacity to keep the temperature of the inverter below a certain temperature below which it is not necessary to limit the torque of the motor in normal operation, it does not necessarily have to transmit the temperature data of the inverter to the control apparatus. However, even in this case, the temperature of the inverter may increase excessively immediately after the cooling apparatus starts to circulate the coolant.
If the capacity of the cooling apparatus is increased to address such a problem, the size and electricity consumption of the inverter may increase beyond tolerable levels.